1. Field of the Invention
The present invention relates to a laser beam machining head. More specifically, the invention relates to a laser beam machining head for feeding a filler wire, or having an electrode for various types of arc welding, such as inert gas shielded tungsten (TIG) arc welding, metal active gas (MAG) arc welding, and plasma arc welding, the head being useful as a tip machining optical system for laser beam machining.
The present invention is also useful when applied to a laser beam machining head of a laser beam machine for cutting or piercing a workpiece of a metal or the like.
2. Description of the Related Art
FIG. 21 is an explanation drawing conceptually showing a composite welding head according to an earlier technology. As shown in the drawing, a composite welding head 223 performs laser welding and TIG welding, and has two welding heads, i.e., a laser welding head 224 and a TIG welding head 225. With such a composite welding head 223, the same site of welding is machined with laser light and a TIG arc, so that it is impossible to set both welding heads 224 and 225 vertically relative to a base material 216. Thus, either the welding head 224 or the welding head 225 is inclined forward or rearward, namely, is given an angle of advance or an angle of backing to carry out welding. In FIG. 21, a tungsten electrode 210 at the tip of the TIG welding head 225 is inclined forward so that an arc 213 will reach a condensing site 206a for a laser beam 206.
FIG. 22 is an explanation drawing conceptually showing a filler wire-coaxial laser welding head 226 according to an earlier technology. As shown in the drawing, the filler wire-coaxial laser welding head 226 has a structure in which a filler wire 207 is passed through holes perforated at the center of a total reflection mirror 214 and an imaging lens system 204. The filler wire 207 and an optical axis of a laser beam are rendered coaxial, and the filler wire-coaxial laser welding head 226 is designed to perform welding while feeding the filler wire 207 via a filler wire feed pipe 208. With the filler wire-coaxial laser welding head 226, a laser beam 206 launched from an optical fiber 201 is reflected by the total reflection mirror 214, and condensed by the imaging lens system 204 for use in fusing a base material 216 and the filler wire 207. The filler wire 207 is fed by a filler wire feeder 209.
FIG. 23 is an explanation drawing conceptually showing a TIG arc-coaxial laser welding head 227 according to an earlier technology. As shown in the drawing, this TIG arc-coaxial laser welding head 227 arranges an electrode 210 for TIG welding and a laser beam optical axis coaxially, thereby performing TIG welding and laser welding simultaneously. Its constitution is basically the same as the constitution of the filler wire-coaxial laser welding head 226 shown in FIG. 22, the difference existing only in the electrode 210, an electrode holding pipe 211 for holding the electrode 210, and a welding power source 212.
FIG. 24 is a vertical sectional view showing the constitution of a tip portion of a conventional, typical laser beam machining head. A laser beam machining head 301 shown in the drawing is provided in a laser beam machine (its machine body is not shown) which cuts an object 302 to be cut, such as carbon steel.
As shown in FIG. 24, a lens-barrel 305 houses a condensing optical system (an imaging lens system) 304 composed of a plurality of lenses 310, and a protective glass 307 for protecting the condensing optical system 304. The condensing optical system 304 condenses laser light 303, and projects it onto a cutting site 302a of the object 302 to be cut. On this occasion, a focal position, f, of the laser light 303 condensed by the condensing optical system 304 is usually adjusted to lie within the object 302 to be cut, as illustrated in the drawing. The laser light 303 is generated by a laser oscillator such as a YAG laser oscillator (not shown), and then transmitted to the condensing optical system 304 by an optical transmission means such as an optical fiber or mirrors (not shown).
On a laser light ejection side of the condensing optical system 304 (i.e., a lower end portion of the lens-barrel 305), an assist gas nozzle 306 is attached in such a manner as to surround the laser light 303 that has been ejected from the condensing optical system 304. The assist gas nozzle 306 is shaped like a truncated cone with a tip side (lower end side) becoming thin, and has an opening 306a at the tip side. To a side surface of the assist gas nozzle 306, an assist gas supply pipe 308 is connected. The assist gas supply pipe 308 is tied to an assist gas supply device (not shown) That is, an assist gas QT transported from the assist gas supply device is introduced into the assist gas nozzle 306 via the assist gas supply pipe 308, and is jetted through the tip opening 306a of the assist gas nozzle 306 toward the cutting site 302a of the object 302 to be cut.
A cutting operation for the object 302 to be cut, by means of the laser beam machine equipped with the laser beam machining head 301 of the above-described constitution, is performed in the following manner: First, the laser beam machining head 301 is brought close to the object 302 to be cut, by the use of a laser beam machining head moving device (not shown). Also, the distance between the tip of the assist gas nozzle 306 and the surface of the object 302 to be cut (i.e., work distance), h, is kept so that there will be no contact between the assist gas nozzle 306 and the object 302 to be cut. In this condition, either the laser beam machining head 301 is moved by the laser beam machining head moving device in a direction perpendicular to the sheet face of FIG. 24, or the object 302 to be cut is moved by a work moving device (not shown) in a direction opposite to the moving direction of the laser beam machining head.
In accordance with this movement, the laser beam machining head 301 condenses the laser light 303 by the condensing optical system 304, and projects it onto the cutting site 302a of the object 302 to be cut, thereby fusing the cutting site 302a. Simultaneously, an assist gas is jetted toward the cutting site 302a from the tip opening 306a of the assist gas nozzle 306, and introduced into the cutting site 302a, to blow away and remove fused metal within the cutting site 302a. Thus, the object 302 to be cut is laser cut.
Of the earlier technologies described above, the composite welding head 223 shown in FIG. 21 has two welding heads, i.e., the laser welding head 224 and the TIG welding head 225. This composite welding head 223 is large in size, and its direction of welding cannot be selected freely, because the two constituent welding heads are at fixed positions, i.e., front and rear positions. Thus, this type of welding head is not suitable for welding an object of a three dimensional shape. With the filler wire-coaxial laser welding head 226 shown in FIG. 22, the center of the laser beam 206 launched from the optical fiber 201 is the site of the strongest intensity distribution of light. This site is the very place where the filler wire feed pipe 208 is situated. The laser beam 206 projected onto the filler wire feed pipe 208 is irregularly reflected, causing a beam transmission loss. Such a laser beam may not be used effectively depending on a purpose to be attained. The TIG arc-coaxial laser welding head 227 shown in FIG. 23, like the filler wire-coaxial laser welding head 226 shown in FIG. 22, poses the problem that the laser beam 206 is irregularly reflected by the electrode holding pipe 211, causing a beam output loss.
The present invention has been accomplished in view of the above-described problems with the earlier technologies. It is an object of the invention to provide a laser beam machining head which can satisfactorily perform welding of an object of a complicated shape, such as a three-dimensional shape, and can also achieve efficient welding without causing a loss in a laser beam projected.
The laser beam machining head of the present invention that attains the above object is characterized by the following:
1) A convex roof mirror and a concave roof mirror are combined to divide a laser beam in two, thereby forming two separate laser beams to be condensed.
2) In the laser beam machining head which is a filler wire- or a TIG, MAG or plasma arc-coaxial laser welding head comprising a filler wire or an electrode for various arcs such as TIG, MAG and plasma arcs, and an optical axis of a laser beam, the filler wire or the electrode and the optical axis being coaxially arranged,
a convex roof mirror and a concave roof mirror are combined to divide the laser beam in two, thereby forming two separate laser beams to be condensed so that no laser beam is projected onto a filler wire feed pipe or an electrode holding pipe.
3) In the laser beam machining head which is a filler wire-coaxial laser welding head comprising a filler wire, and an optical axis of a laser beam,
a convex roof mirror and a concave roof mirror are combined to divide the laser beam in two, thereby forming two separate laser beams to be condensed, with spacing being present between the two separate laser beams, and the filler wire is fed to a condensing position via a filler wire guide in the spacing between the two separate laser beams from a filler wire feed pipe disposed outside the laser beams.
4) In the laser beam machining head which is a TIG, MAG or plasma arc-coaxial laser welding head comprising an electrode for various arcs such as TIG, MAG and plasma arcs and an optical axis of a laser beam,
a convex roof mirror and a concave roof mirror are combined to divide the laser beam in two, thereby forming two separate laser beams to be condensed, with spacing being present between the two separate laser beams, and a tip of the electrode is held above a condensing position while the electrode is supported by a water flow pipe or an electrode holding pipe passing through the spacing between the laser beams.
5) In the laser beam machining head recited in 1), 2), 3) or 4) above, the ratio of the intensities of the two separate laser beams, or the position of the laser beam may be changed by making the position of an optical fiber for laser beam transmission, or the convex roof mirror and the concave roof mirror, movable relative to a lens center in two directions perpendicular to the optical axis in a plane perpendicular to the optical axis.
In laser cutting using an assist gas as shown in FIG. 24, the manner of flowing the assist gas to the cutting site 302a, i.e., the flow velocity and flow rate of the assist gas jetted at the cutting site 302a, greatly affect cutting performance.
With the conventional laser beam machining head 301, as shown in FIG. 25, the diameter of the opening (the width of the opening), d, of the assist gas nozzle 306 is considerably greater than the cutting width (kerf width), w, (in laser cutting, the cutting width w is as small as, say, 2 to 3 mm). Thus, the entire assist gas QT jetted from the assist gas nozzle 306 is divided into an assist gas Q2 which is fed into the cutting site 302a, and assist gases Q3, Q4 which flow to both sides of the cutting site 302a through the clearance between the assist gas nozzle 306 and the object 302 to be cut. That is, only a part of the assist gas QT introduced into the assist gas nozzle 306 (i.e., assist gas Q2) flows into the cutting site 302a, resulting in a small flow rate of assist gas which contributes to cutting. Hence, the efficiency of removal of fused metal by the assist gas is so low that the cutting performance is low. Furthermore, the gas pressure cannot be increased, because of restrictions imposed by the pressure-resistant strength of the optical parts.
As shown in FIG. 26, the tip opening 306a of the assist gas nozzle 306 may be thinned, in comparison with the earlier technologies, to make the opening diameter d and the cutting width W nearly equal. By so doing, most of the assist gas introduced into the assist gas nozzle 306 flows into the cutting site 302a, and the velocity of the assist gas jetted becomes greater than before. In addition, as is known in hydrodynamics, a zone with a length L ( greater than 4d) in a tip portion of the assist gas nozzle 306 may be set at a constant internal diameter, d. This stabilizes the flow of the assist gas, increasing its directivity.
In this case, however, part of the laser light 303 interferes with an inner surface 306b of the assist gas nozzle 306 (i.e., a shaded portion in FIG. 26) at the tip portion of the assist gas nozzle 306. As a result, its thermal energy is absorbed, or the partial light is irregularly reflected, causing the directivity of the laser light 303 to be lost. Hence, the laser light 303 is not projected effectively onto the object 302 to be cut, with the result that the cutting performance is decreased. In other words, the opening diameter d of the assist gas nozzle 306 is restricted by the breadth of the laser light 303 at the tip opening 306a, and thus cannot be made smaller than the width over which the laser light 303 broadens.
As indicated by a pattern of a cut surface shown in FIG. 27, when the object 302 to be cut is cut in a direction of an arrow G, for example, the pattern at the cutting site 302a points obliquely in a direction opposite to the direction of cutting. Thus, a substantial thickness of the plate to be cut increases compared with the actual plate thickness T, resulting in a decrease in the cutting ability.
This tendency appears more clearly as the plate thickness T increases. This is because with increasing plate thickness T, the penetrating ability for the plate thickness T (the ability to fuse the object 302 to be cut, by heat and penetrate through it) lowers; at a deep position in the direction of plate thickness, moreover, the ability of the assist gas to remove fused metal also declines, so that fused metal tends to flow in the direction opposite to cutting without flowing downwards. If the plate thickness T becomes even greater, and this tendency becomes even stronger, the object 302 to be cut cannot be cut any more.
The cutting ability of the laser light 303 for the object 302 to be cut is affected by the position of the focal position f of the laser light 303 relative to the object 302 to be cut. Customary practice has been to adjust the focal position f of the laser light 303 to rest in the interior, in the direction of plate thickness, of the object 302 to be cut, as shown in FIG. 24. If this focal position f can be suitably adjusted depending on the material and thickness of the object 302 to be cut, an increase in the cutting performance can be expected. However, if it is attempted to change the focal position f of the laser light 303 by moving the laser beam machining head 301 in the direction of plate thickness, the assist gas nozzle 306 also moves in the direction of plate thickness to change the distance between the assist gas nozzle 306 and the object 302 to be cut. Consequently, there may be a decrease in the ability of the assist gas to remove fused metal.
From the point of view of the ability of the assist gas to remove fused metal, the assist gas nozzle 306 should be made as close as possible to the object 302 to be cut. If the laser beam machining head 301 is moved upward in FIG. 24 to move upward the focal position f of the laser light 303 relative to the object 302 to be cut, the assist gas nozzle 306 also moves upward accordingly, increasing the spacing h between the assist gas nozzle 306 and the object 302 to be cut. Thus, the ability of the assist gas to remove fused metal lowers. If the assist gas nozzle 306 is brought close to the object 302 to be cut, by contrast, the focal position f of the laser light 303 relative to the object 302 to be cut is moved, and the assist gas nozzle 306 interferes with the object 302 to be cut.
In the light of these problems, it is another object of the present invention to provide a laser beam machining head which can increase the ability of an assist gas to remove fused matter, such as fused metal, by efficiently feeding the assist gas into a machining site (a cutting site or a piercing site) of a workpiece to be cut or pierced, and also increasing a jet velocity of the assist gas.
It is still another object of the invention to provide a laser beam machining head which can efficiently feed the assist gas into the machining site, increase a jet velocity of the assist gas, and increase a jet flow rate of the assist gas.
It is a further object of the invention to provide a laser beam machining head which can remove the fused matter more efficiently (can make the substantial thickness of a plate to be cut, close to the actual plate thickness) from a cutting site of an object to be cut, by jetting an assist gas at the cutting site obliquely relative to the direction of cutting.
It is a still further object of the invention to provide a laser beam machining head which can make the substantial thickness of a plate to be cut, close to the actual plate thickness by adjusting the direction of a jet of an assist gas toward the cutting site of the object to be cut, to be an optimal direction.
It is an additional object of the invention to provide a laser beam machining head which can increase the machining ability of laser light by adjusting the position of the assist gas nozzle relative to the workpiece, or the focal position of the laser light relative to the workpiece, independently to be an optimal position.
It is an even additional object of the invention to provide a laser beam machining head which can protect a condensing optical system reliably.
Therefore, the laser beam machining head of the present invention that solves the aforementioned problems is characterized by the following:
6) A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprising:
a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams;
a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and
an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, or a hole diameter of the piercing site.
7) A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprising:
a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams;
a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and
an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, and a length of the opening of the tip portion being larger than the width of the opening.
8) A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprising:
a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams;
a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and
an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, and a tip side of the inner assist gas nozzle being inclined in a direction of cutting.
9) The laser beam machining head of 8) above, wherein an angle of inclination of the inner assist gas nozzle can be varied independently of a direction of projection of the laser light.
10) A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprising:
a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams;
a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and
an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, or a hole diameter of the piercing site, and wherein:
relative positions of the inner assist gas nozzle and the workpiece can be varied independently of relative positions of a focal position of the condensing optical system and the workpiece; or the relative positions of the focal position of the condensing optical system and the workpiece can be varied independently of the relative positions of the inner assist gas nozzle and the workpiece.
11) In the laser beam machining head described in 6), 7), 8), 9) or 10), an outer assist gas nozzle may be provided at an exit side of the condensing optical system so as to surround the separate laser beams launched from the condensing optical system, and the assist gas may also be jetted through a tip opening of the outer assist gas nozzle.